Vibration damped sandwich systems having interlayers of vinyl acetate/2-ethylhexyl acrylate/dibutyl maleate/crotonic acid copolymers

ABSTRACT

A VIBRATION DAMPED SANDWICH SYSTEM COMPRISING TWO HARD PLATES AND INTERPOSED BETWEEN THE PLATES A VIBRATION DAMPING INTERLAYER COMPRISING A COPOLYMER OF 30 TO 40% BY WEIGHT OF VINYL ACETATE, 30 TO 40% BY WEIGHT OF 2-ETHYL-HEXYL ACRYLATE, 30 TO 10% BY WEIGHT OF DIBUTYL MALEATE AND 5 TO 15% BY WEIGHT OF CROTONIC ACID.

July 4, 1972 Filed Dec. 14, 1970 H. OBERST ETAL VIBRATION DAMPEDSANDWICH SYSTEMS HAVING INTERLAYERS OF VINYL ACETATE/Z-ETHYLHEXYLACRYLATE/DIBUTYL MALEATE/CROTONIC ACID COPOLYMERS 3 Sheets-Sheet 1 FIG.1a 1.0

05 1 w l dcomb FIG. 1b 1.0

dcomb ///A-\\ Hz Om 0 +20 +40 +60 +80 0c INVENTORS HERMANN 52 1 ilk-(mm;(l y,

GUNTHER KLUIE ALFRED SCHOMMER ATTORNEYS July 4, 1972 H. OBERST ETAL3,674,624

VIBRATION DAMPED SANDWICH SYSTEMS HAVING INTERLAYERS OF VINYLACETATE/Z-ETHYLHEXYL ACRYLATE/DIBUTYL MALEA'I'E/CROTONIC ACID GOPOLYMERSFiled Dec. 14, 1.970 3 Sheets-Sheet 2 FlG.1c

O5 100 H. comb INVENTORS HERMANN CEqTPi ,Cl-Lrm 53: GUNTHER DUVE ALFREDSCHOMMER BY M r ATTORNEYS July 4, 1972 H. OBERST ETAL 3,674,624

VIBRATION DAMPED SANDWICH SYSTEMS HAVING INTERLAYERS OF VINYLACETATE/Z-ETHYLHEXYL ACRYLATE/DIBUTYL MALEATE/CROTONIC ACID COPOLYMERSFiled Dec. 14, 1.970 3 Sheets-Sheet 5 INVENTORS HEM A ins-PW? GUNTHERDUJE ALFRED SCHOMMER M,M W

ATTORNEYS United States Patent F 50,757 Int. Cl. B32b 15/08; C081?15/20; E04b 1/86 U.S. Cl. 161-165 4 Claims ABSTRACT OF THE DISCLOSURE Avibration damped sandwich system comprising two hard plates andinterposed between the plates a vibration damping interlayer comprisinga copolymer of 30 to 40% by weight of vinyl acetate, 30 to 40% by weightof 2-ethyl-hexyl acrylate, 30 to 10% by weight of dibutyl maleate and 5to 15% by weight of crotonic acid.

This application is a continuation-impart of application Ser. No.684,739 filed Nov. 21, 1967, and now abandoned.

The present invention provides vibration damped sandwich systems havinginterlayers made of vinyl acetate/2- ethyl-hexyl acrylate/dibutylmaleate/crotonic acid copolymers.

It is known from South African specification No. 5,269 that highlyvaluable vibration damping materials of a broad temperature bandsuitable for damping bending vibrations of metal sheet constructions canbe produced by copolymerizing monomers whose homopolymers differ intheir second order transition temperature by at least 20 C. The abovespecification also reports that as vibration damping materials having abroad temperature band there can be used, among others, predominantlyamorphous copolymers of esters of alcohols with 4 to 12 carbon atomswith acrylic and maleic acid and vinyl esters of fatty acids with 2 to 3carbon atoms, for example, vinyl acetate/Z-ethylhexylacrylate and/ordibutylmaleate copolymers.

It has now been found that copolymers of vinyl acetate, suitable estersof unsaturated polymerizable carboxylic acids and an unsaturatedcopolymerizable acid, preferably crotonic acid, have outstanding dampingproperties and are especially suitable for the vibration damping ofsandwich systems of hard plates, in particular metal sheets. Suitableesters are especially those of acrylic acid and maleic acid with alcoholcomponents having 3 to 9 carbon atoms, preferably 2-ethyl-hexyl-acrylateand dibutyl maleate. With these copolymers, the vibration damping effectof which critically depends on the weight proportion of the monomers,very broad damping curves can be obtained having very high maximumdamping values. From the economical point of view they have theadvantage of being rather cheap.

Copolymers consisting of 30 to 40% by weight of vinyl ice acetate, 30 to40% by weight of Z-ethyl-hexyl acrylate, 30 to 10% by weight of dibutylmaleate and approximately 10% by weight of crotonic acid constituteexcellent broad band damping materials which can be used in a largerange of temperature.

The present invention provides sandwich systems of hard plates, inparticular metal sheets, having vibration damping, self-adherentinterlayers of vinyl acetate/Z-ethylhexyl acrylate/dibutylmaleate/crotonic acid copolymers, for which interlayers there are usedcopolymers consisting of 30 to 40% by weight of vinyl acetate, 30 to 40%by weight of 2-ethyl-hexyl acrylate, 30 to 10% by weight of dibutylmaleate and 5 to 15% by weight of crotonic acid.

A copolymer having satisfactory vibration damping characteristics wasprepared according to the procedure set forth in Example I below.

EXAMPLE I A mixture composed of 35 g. (34.3%) vinyl acetate 35 g. (34.2%2-ethyl hexylacrylate 20 g. (19.6%) di-n-butylmaleate 10 g. (9.8%)crotonic acid 5 g. isopropanol and 2 g. (1.96%) dibenzoyl peroxide (ofapprox. 72.8%

strength) was slowly heated in glass reaction vessel provided withreflux condenser and thermometer. When the temperature had reachedapproximately C., refluxing commenced, and at a temperature ofapproximately C. the increased viscosity showed that polymerization hadstarted. The temperature was raised to C. and maintained at this levelfor 1 hours, and then the residual monomer was distilled off underreduced pressure. The polymer was light-colored to colorless, soluble inethyl acetate (clear) and in NH aq. (milky). The acid number was 45.4mg. KOH/g. substance and the K value (2% in ethyl acetate, at 20 C.) was27.2. The molecular weight was about 46,000.

FIGS. 1a to 10 of the accompanying drawings are plots againsttemperature of the loss factor d to illustrate the superior efficiencyof the novel systems. The curves in FIGS. 1a and 112 show the lossfactor dcomb of two metal sheet arrangements of the invention as afunction of temperature. For comparison one of the most effectivevibration damping materials known for metal sheet arrangements was used,namely a copolymer of 63% by weight of vinyl acetate and 37% by weightof dibutyl maleate containing as plasticizer 15% by weight of 2-ethylhexyl phthalate and 15% by weight of tricresyl phosphate,calculated on the mixture (curve FIG. 10). The copolymer of curve 10 wasa thermoplastic adhesive especially suitable for preparing vibrationdamped metal sheet sandwich systems comprising two outer metal sheetsand a self-adherent thermoplast as damping interlayer. Systerns of thistype provide a damping effect which is extremely high in its maximum andcannot be exceeded for physical reasons (cf. H. Oberst and A. Schommer,Kunststoffe, volume 55, page 634 (1965), especially FIG. 9). In asymmetrical arrangement comprising two metal sheets, each having athickness of 0.5 millimeter, and an interlayer 0.3 millimeter thick theloss factor dcomb of the combined system, measured in the bending wavemethod (cf. for example H. Oberst, L. Bohn and F. Lindhardt,Kunststoife, volume 51, page 495 (1961)), almost reaches the value dcombof l. The known metal sheet damping by oneside damping coatings whichare applied by spraying, trowelling or bonding in the form of layers ofso-called vibration damping materials show loss factors generally ofless than d =0.2 with technically reasonable thicknesses or ratios ofcoating mass to plate mass of the combined system. With metal sheetsandwich systems which gain growing importance in recent times, it ispossible to obtain damping values that are increased by a a multiple, asshown by the present example, when the interlayer material has theappropriate composition and thickness.

The temperature band width of the damping in the metal sheet sandwichsystem does not only depend on the viscoelastic properties of theinterlayer and the steel sheets but also to a considerable extent on thegeometry of the arrangement, i.e. on the ratio of the layer thicknesses(cf. loc. cit. (1965), FIGS. 8 to 10). With metal sheet sandwich systemsthe band width is advantageously defined as the range of the temperatureinterval within which the value d =0.05 is exceeded. The damping ofmetal sheets which are not damping by additional vibration damping meansin metal sheet constructions of various types corresponds to values d =land less. The reference value dcomb of 0.05 thus means a considerableincrease in the damping effect (by about 15 db (decibel)) as compared tothe nil damping d =0.01.

In the curve shown in FIG. 1c the reference value dcomb of 0.05 isexceeded in the mainly interesting frequency range of from 100 to 1,000cps. (Hz.) at temperatures ranging from about 0 to 50 C. The temperatureband width thus corresponds to about 50 C. Sandwich systems of this typeare, therefore, suitable for many technical fields of application. Bymodifying the content of plasticizer, it is possible to shift thetemperature band of a high damping effect to higher temperatures andthus to adapt the material to special technical uses, for example inmachine units operating at elevated temperatures. This example of ametal sheet sandwich system comprises a self-adherent interlayer havingoptimum properties of a vibration damping material with a broadtemperature band prepared by copolymerizing appropriate monomericcompounds has hitherto not been surpassed by other arrangements ofsimilar kind and may be taken as standard for judging the acousticefficiency of the system according to the invention.

FIGS. 1a, lb and 1c show the temperature curves of the loss factor dcombof metal sheet sandwich systems comprising steel sheets of a thicknessof 0.5 millimeter each and damping interlayers of a thickness of 0.3millimeter, and 0.7 millimeter, respectively (FIG. 1b) for a frequencyof 100 and 1,000 cps.

The curves were measured with sandwich systems the interlayers of whichconsisted of (la) a copolymer of 30% by weight of vinyl acetate, 30% byweight of 2-ethyl-hexyl acrylate, 30% by weight of dibutyl maleate and10% by weight of crotonic acid (according to the invention),

(1b) a copolymer of 35% by weight of vinyl acetate, 35% by weight ofZ-ethyl-hexyl acrylate, 20% by weight of dibutyl maleate and 10% byweight of crotonic acid (according to the invention),

(1c) a copolymer of 63% by weight of vinyl acetate and 37% by weight ofdibutyl maleate containing 15% by weight of Z-ethyl-hexyl phthalate and15% by Weight of tricresyl phosphate, both calculated on the mixture.

The arrangement 1a and 1b, whose monomer proportions lie in the optimumrange have very broad temperature band widths with relatively highmaximum damping value. The fact that the maximum values are not so highas in curve 1c is compensated by the large band widths. With thearrangement 1a the center of the damping is at 15 to 25 C. with maximumdamping values of about 0.5 to 0.6. The temperature band Width is aboutC. for cps. and about 70 C. for 1,000 cps. Towards low temperatures thefield of application reaches to 10 C. The excellent vibration dampingproperties are maintained up to a mean temperature of about +65 C. Withthe arrangement 1b the damping center lies in a temperature range from20 to 25 C. with maximum values of dcomb of 0.4 to 0.6. The temperatureband width is about 100 C. for 100 cps. and 80 C. for 1,000 cps. As inarrangement 1a, the slow decrease of the damping towards hightemperatures at 100 cps. is especially favourable. The reference valuedcomb +0.05 is exceeded at a temperature in the range of from about 15to +80 C. As compared with the standard system 10, arrangements 1a and1b with broader temperature band widths have more favourable dampingproperties at temperatures below 0 C. and about 50 C. so that they aresuitable for quite a number of applications. Moreover, owing to theircontent of 10% by weight of crotonic acid the copolymers used inarrangements 1a and 1b can be cross-linked by reaction with abifunctional or trifunctional compound (for example, a compoundcontaining a plurality of epoxide or isocyanate groups), whereby thesoftening range and therewith the range of high damping can benoticeably shifted towards higher temperatures.

A special advantage of the vibration damping material of the presentinvention resides in the fact that it may be applied continuously duringthe mass production of the metal sheet sandwich systems. It is athermoplastic adhesive which may be applied to the metal sheets bytrowelling, brushing or pouring at elevated temperature. The sandwichsystem may then be advantageously cooled under pressure between rollers.Except for degreasing the metal sheets require no preliminary treatmentand no other adhesive. Owing to the content of the copolymers ofcrotonic acid degreasing may even be dispensed with. The adhesion isvery good.

The vibration damping material of the present invention has a goodresistance to flow. The metal sheet sandwich systems may, within broadlimits, be processed as normal metal sheets, that is they may becreased, bent, shaped, welded and riveted. In this manner laminatedsystems are obtained which are of universal application. They have adamping height and a temperature range of damping which are wellsuitable for many applications, in particular also at low temperaturesbelow 0 C.

Minor amounts of fillers, for example, for improving the electricconductivity (improvement of resistance welding) may be incorporated inthe vibration damping materials. In order not to affect the dampingeffect adversely it is advantageous to use less than 1% by weight,preferably less than 0.5% by weight of filler, calculated on thecopolymer. Suitable fillers are, for example, heavy spar, silicic acid,graphite and soot.

The metal sheet sandwich system suitably has a total thickness in therange of from 1 to 6 millimeters, preferably 0.2 to 0.5 millimeter. Amaximum damping effect is obtained with symmetrical laminated systems.With an equal weight, asymmetrical laminated systems have, however, ahigher stiffness in flexure and a higher strength. Asymmetricallaminated systems are, therefore, preferred for those applications whichrequire a high strength with respect to the weight. The ratio of thethickness of the outer plates or metal sheets is preferably within therange of from 1:1 to 1:4.

FIG. 2 of the accompanying drawings shows sandwich systems withsymmetrical arrangement (a) and asymmetrical arrangement (b) in whichthe interlayer 2 is interposed between the two outer plates or metalsheets 1.

in claim 1, wherein the copolymer of the interlayer contains up to 1% byweight of a filler, calculated on the copolymer.

4. A vibration damped sandwich system as claimed in claim 1, wherein theratio of the thicknesses of the hard plates lies preferably in the rangeof from 1:1 to 1:4.

6 References Cited UNITED STATES PATENTS 3,271,181 9/1966 Albert et a1.1612l8 3,275,589 9/1966 Alexander et a1. 26078.5 E 3,311,595 3/1967Kahrs et a1. 260-785 E 3,399,103 8/1968 Salyer et al 161-218 3,423,352I/ 1969 Levine et a1 26078.5 E 3,446,767 5/1969 Nolan 260-785 E JOHN T.GOOLKASIAN, Primary Examiner G. W. MOXON II, Assistant Examiner US. Cl.X.R.

161-216, 218; 181--33 G, 33 GA; 248-21; 260-41 A, 78.5 E, 80. 8, 80.81

